This invention generally relates to luminal graft endoprostheses or endovascular grafts which have the ability to carry out dilation and/or support functions. These devices are suitable for treating blood vessel lesions and the like. An expandable endovascular prosthesis tubular support component and elastomeric graft material are combined into a single device wherein the graft material is secured to either or both of the internal and external surfaces of the expandable endoprosthesis. The graft material preferably is produced by a spinning technique such as that described in U.S. Pat. No. 4,475,972, the subject matter thereof incorporated by reference hereinto.
In summary, the luminal graft endoprosthesis includes a tubular support with an internal surface and an external surface. It is expandable from a first diameter to a second diameter which is greater than the first. When it is in its first diameter, the tubular support is of a size and shape suitable to be inserted into human or animal body pathways. An expandable coating, made from a substantially inert biocompatible graft material is applied onto at least one of the surfaces or walls of the tubular support element.
Luminal endoprostheses with expandable coating on the surface of external walls of radially expansible tubular supports are proposed in U.S. Pat. Nos. 4,739,762 and No. 4,776,337. In these two patents, the manufacturing process is not described and the coating is made from thin elastic polyurethane, Teflon film or a film of an inert biocompatible material. Such film may have radially projecting ribs for fixation, and macroscopic openings, via which the blood can flow between the covering and the vessel in which the endoprosthesis is anchored. Correspondingly, a coating formed from an elastomeric polyurethane film has been applied around a metallic support with form memory properties. See A. Balko et al., "Transfemoral Placement of Intraluminal Polyurethane Prosthesis for Abdominal Aortic Aneurysm", Journal of Surgical Research, 40, 305-309, 1986. In U.S. Pat. Nos. 5,019,090 and No. 5,092,877, the possibility of covering the support of a radially expansible endoprosthesis is generally mentioned but not described.
All of the luminal endoprostheses made according to these previous approaches have the disadvantage that the material used is not sufficiently biocompatible. In fact, expansible tubular supports have existed for a long time, for example, supports used solely to keep the mouths of certain weak vessels open. It should especially be mentioned that there are supports or stents which are expanded by applying an exterior force, e.g. inflating a balloon located inside the support. See for example U.S. Pat. Nos. 4,733,665, No. 4,739,762, No. 4,776,337, No. 4,800,882 and No. 5,019,090. As is the case with other supports, it must be noted that some of these are auto-expansible due to their elasticity (see particularly U.S. Pat. No. 4,580,568 and the supports placed onto the market by Pfizer under the WALLSTENT.RTM. name), or due to their form memory properties (supports placed onto the market under the NITINOL name).
Other prior approaches include semi-rigid prostheses introduced endoluminally. These prostheses have the form of full tubes which can be connected to vessels to be reinforced by means of end supports such as those mentioned above. See for example U.S. Pat. No. 4,140,126, No. 4,787,899 and No. 5,104,399 and J. C. Parodi et al., "Transfemoral Intraluminal Graft Implantation for Abdominal Aortic Aneurysms", Annals of Vascular Surgery, Vol. 5, No. 6, 1991.
Based on actual experience, when supports have been used alone, it has been shown that they lead to unorganized development of the cells in the mesh of the support, with rapid reforming of the cellular thickening in the vessels to be protected, i.e. fibrous hyperplasia. On the other hand, the tubes introduced as endoprostheses are used without a supporting element. Thus, a certain degree of rigidity must be offered. Their structures make them inappropriate in terms of the cellular growth on their walls. For the same reasons, expandable endoprostheses with an expandable coated support are inappropriate for normal growth of cells. They continue to represent a foreign body on the inside of the human or animal body into which they are implanted and, because of the films used, no normal cellular invasion is possible on the inside of their structure.
There are tube-formed prostheses made from fibrous material having a structure of superimposed layers of fibers, where the fibers of one layer intersect those of neighboring layers, and a manufacturing process for such prostheses has been described. See J. Leidner et al., "A Novel Process For the Manufacturing of Porous Grafts: Process Description and Product Evaluation", Journal of Biomedical Materials Research, Vol. 17, 229-247 (1983). These prostheses are used to replace fragments of defective vessels. Radial expansion of these prostheses is not necessary and is usually disadvantageous in view of the internal blood pressure. Generally, there are approximately 400 superimposed layers of successively interlaced fibers.
To solve these problems, in accordance with this invention, a luminal endoprosthesis is provided with an expansible coating made from fibrous material. The fibers of this fibrous material form a structure among themselves which facilitates normal cellular invasion, without stenosis or recurrent stenosis of the human or animal pathway when the supporting element is in its second or expanded diameter. Surprisingly, it has been found that fibrous material, in which the openings between the fibers are greater than 30.mu., preferably at least 50.mu., when the element is in its second diameter, not only facilitates cellular invasion, but also achieves particularly normal cellular growth with perfect cohabitation between cells and compatible biological fibers.
According to an implementation form of this invention, the fibers of the fibrous material are oriented at an angle less than 50.degree., often less than 30.degree., with respect to a generator of the tubular support element, when the latter is in its first diameter. Advantageously, the fibrous material is elastic. Preferably, polycarbonate fibers or polycarbonate urethane fibers are used, although other materials are possible. For example, polycarbonate polyurethane fibers placed onto the market by Corvita Corporation under the name CORETHANE.RTM. are especially suitable. When such a fibrous coating is used, the diameter of its cylinder shape can be extended by 2 to 4 times with a concommitment change in wrap angle from 30.degree. to 50.degree. to 50.degree. to 90.degree.. According to an advantageous implementation form of this invention, the fibers of the fibrous material have a diameter to 10.mu. to 20.mu. and are arranged in several superimposed layers.
According to the preferred form of this invention, the support has an expandable covering which is applied onto or adhered to the surface of the external wall of the support element and/or onto the surface of the internal wall. It is also possible to consider reinforced endoprostheses, in which the support element does not come into contact with the human or animal tissue, which embodiment is accomplished by incorporating the support structure into the wall of the graft. This results in improved biocompatibility.
The process for manufacturing an endoprosthesis according to this invention applies to an expandable, fibrous cover onto at least one of the surfaces of the wall of the support element. When the support element is at its first diameter, the device has a predetermined fibrous structure. When the support element is at its second diameter, the openings between the fibers of the fibrous material are greater than 30.mu. and preferably at least 50.mu.. This process is preferably employed when a tubular support or endoprosthesis that is expandable by an internal force is used, for example one that is deployed by inflating with a balloon.
In an alternative approach, an expandable, fibrous covering with a predetermined fibrous structure is applied to at least one of the surfaces of the wall of a support element having a third diameter, equal to or greater than its second diameter. When the support element is in its second diameter, the openings between the fibers of the fibrous material are greater than 30.mu. and preferably at least 50.mu.. The wrap angle in its second diameter is 40.degree. to 70.degree.. The thus covered support element is longitudinally stretched to its first diameter where the wrap angle is reduced to 20.degree. to 30.degree. and introduced to the body in this first diameter configuration. Introduction is performed by pushing the longitudinally stretched structure out of the lumen of a catheter, at which point the structure self expands to its second diameter. This approach is especially suitable when a self-expanding or auto-expandable, such as a spring-loaded type, of tubular support is used.